The present invention relates to a driving arrangement and, more particularly, to a hydraulic driving arrangement for positioning workpieces in a correct relationship to tool heads of a machine tool having a plurality of stations arranged at preferably equal angular spacings about an axis of a circular indexing table, and with the workpieces being subject to a sequence of different processing operations carried out at the different working stations and cyclically advanced from working station to working station, with an exact position of the workpieces being defined by an index. A circular indexing table being movable to an approximate position, within predetermined tolerances, enters into a locking engagement with one of a plurality of index bodies associated with different positions of the circular indexing table so as to move and retain the workpieces in the correct position relative to the individual tools required for precise processing.
For positioning workpieces in an exact relationship with respect to a plurality of working station axes, a Geneva gear is normally employed due to the quickness and precision of such a Geneva drive; however, a disadvantage of a Geneva drive resides in the fact that they are very expensive to produce. Moreover, it is an operational disadvantage of Geneva drives that workpieces can be indexed only by a predetermined step size. Thus, for example, if one or more working stations are to be skipped, it is necessary to accelerate and stop, for example, the circular indexing table a corresponding number of times thereby resulting in relatively long overall cycle times.
The aim underlying the present invention essentially resides in providing a hydraulic drive arrangement of the aforementioned type which avoids the above noted disadvantages, ensuring precise positioning of the workpieces.
In accordance with advantageous features of the present invention, the circular indexing able is driven by a hydraulic motor which is controlled by an electro-hydraulic follow-up governor using a stepping motor for setting the desired values and mechanical actual value indication means. Monitoring means are provided which are positively coupled with the circular indexing table and/or a driving gear of the hydraulic motor and which indicate whether or not the circular indexing table is in a position suitable for bringing an indexing gear into engagement and, if so, emits a signal triggering the indexing process. If the circular indexing table is not in a suitable position, the monitoring means deactivates the indexing mechanism.
By virtue of the above noted features of the present invention, the governor-controlled hydraulic drive permits the motion sequence to be controlled as desired within broad limits, with regard to acceleration, maximum feeding speed and braking. Furthermore, high positioning accuracies and rapid cycle sequences may be achieved.
In accordance with further features of the present invention a monitoring means includes a cam disk coupled with the circular indexing table through a gearing fro insuring that it performs exactly a full rotation of 360.degree. when the circular indexing table moves from a first position suited for processing of the workpiece into the next position. By virtue of this arrangement, it is possible to permit the implementation of a monitoring arrangement by simple technical means. This monitoring arrangement uses an index for monitoring and/or controlling the indexing movements into predetermined positions in a reliable manner.
In order to provide a very simple monitoring disk construction used within the monitoring device, in accordance with still further features of the present invention, a cam disk is provided which includes at least three leading edges which trigger a signal when passing an inductive pick-up provided as position detectors. The first leading edge triggers a high level output signal when passing the associated detector when the circular indexing table reaches a position in which the engagement of the index is possible, but the exact desired position of the circular indexing table has not yet been reached. The second leading edge triggers a high level output signal when passing an inductive pick-up as soon as the exact desired position of the circular indexing table is reached and the circular indexing table starts running beyond the desired position. The third leading edge triggers a high level signal at an inductive pick-up when the circular indexing table has run beyond the angular area suitable for indexing.
It is also possible in accordance with the present invention to advantageously provide an absolute position indicator as part of the monitoring device to permit monitoring of the indexing motion in accordance with freely predetermined desired positions.
Further details, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings.